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Porifera (Sponges)

Sponges (Phylum Porifera) are a group of simple aquatic invertebrates that include three groups - Glass sponges, Demosponges and Calcareous sponges. There are about 5,000 to 10,000 species of sponges found mostly in marine environments with about 100 species of freshwater sponges.

They are found in a very wide range of habitats from tidal zones to amost 9,000 metres depth and from the polar regions to the tropics. Most live in quiet, clear waters, because sediment stirred up by waves or currents would block their pores, making it difficult for them to feed and breathe. Most sponges are anchored to hard surfaces like rocks, but some sponges can attach themselves to soft sediments using a root-like base.

Adult sponges can be asymmetrical or radially symmetrical and come in a variety of sizes, colours, and shapes including tree-like, fan-shaped, cup shaped, tube shaped, ball shaped and shapeless.

Diversity in Porifera

The Demosponges are often brightly colored and grow to be the largest of all sponges, they make up more than 90% of all sponge species. The Calcareous sponges (about 100 species) have spicules that are made of calcium carbonat and are often smaller than other sponges. Glass sponges (about 500 species) have spicules made from silica, most are found at depths of 450 to 900 metres and are common in colder Antarctic waters.

A spicule small needle-like structure made from silica, spongin (a type of collagen protein similar to the keratin of hair and fur) or calcium carbonate which helps support the soft tissue of sponges and deter predators. They come in a variety of shapes and sizes.

Spicules of sponges (highly magnified)

Most sponges are filter feeders, eating bacteria and other food particles in the water. The volume of water passing through a sponge can be huge, up to 20,000 times the sponge's volume in a 24 hour period. Some sponges contain photosynthesitic micro-organisms (like corals do) in their bodies. A few species of sponge are carnivorous preying mainly on small crustaceans and other small animals.

A few species of fish, seaslugs and hawksbill turtles eat sponges, many sponge species contain toxic substances as well as sharp spicules to discourage predators.

Azure vase sponge (Callyspongia plicifera)
A demosponge



Volcano sponge with brittle star
Image © Allison Finch Flickr

The wonderful world of the sea sponges- The Abyss- BBC Wildlife
Kate Humble ventures down the Cayman wall, described as the Himalayas
beneath the waves and including one mountain 5 miles deep. At 500 feet
down, she experiences the wonderful world of the sea sponge. These
creatures are some of the only animals on earth with no dependence on
sunlight and act like swiming pool filters cleaning up to 20 lites of water
per day. Check out the amazing shapes and types of sea sponge in
this magical video from BBC wildlife show 'The Abyss'.

Next: Structure of sponges  ...   


Structure of sponges
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